For a long time paper has been used for recording various information, and even now a lot of information is recorded on paper. On the other hand, along with industrial growth, film (e.g. microfilm) for recording image information, such as moving images and still images, phonograph records for recording sound and the like have begun to be used, and in recent years, optically readable optical recording media, semiconductor recording media and the like, including magnetic recording media, CD, DVD and optical cards, are used as media for recording digital data.
Some information recorded on the above mentioned media are demanded to be stored for a very long time, beyond 100 years. The above mentioned media has durability for not causing problems in terms of the respective intended use, and such media as paper, film and phonograph records, for example, have sufficient durability on a time scale of several years. However, on a time scale exceeding 100 years, time related deterioration is inevitable, and stored information may be lost or damaged by water and heat. For example, in the case of microfilm constituted by cellulose acetate, vinegar syndrome occurs, that is, the film decomposes depending on the temperature and humidity of the storage environment, and acetic acid is generated on the surface of the film, which makes it impossible to read out data. Therefore the life of microfilm is regarded as 30 years or less. In the case of microfilm constituted by polyester, life is regarded to be about 500 years, but this is implemented only when the microfilm is stored in an environment specified by ISO and JIS standards. In other words, the storage environment is still one risk factor in losing information.
Magnetic recording media, optical recording media, semiconductor recording media and the like have sufficient durability with which no problem occurs when using standard electronic apparatuses, but such media are not designed considering a time scale of several decades, hence they are inappropriate for the permanent or semipermanent storage of information. For example, in the case of EEPROM, represented by flash memory, which is a semiconductor-based recording medium, data is recorded and stored by holding charges using floating gates, and the time of holding charges by floating gates is influenced by the storage environment. Further, the insulating layer may be damaged by repeatedly writing data, whereby holding charges may become impossible. ROM is known as a long life semiconductor recording medium, but cost is exorbitant to reproduce ROM as a backup.
Another problem of the above mentioned media is that fire resistance and heat resistance are low. For example, if fire occurs in a location where the above mentioned recording media exists, the data thereof is lost due to heat. In other words, it is virtually impossible to permanently or semipermanently store information using the currently available media.
As a method for permanently or semipermanently storing information, a method of recording and storing information in a media having durability, such as quartz glass, was proposed (see PTL 1 and 2). In concrete terms, the proposed methods are: a method for three-dimensionally recording data in micro cells in a cylindrical medium utilizing the difference of light transmittance, and reading out the information while rotating this medium based on the computer tomography technique (see PTL 1); and a method of irradiating an electromagnetic wave to a cylindrical medium while changing the irradiation angle and measuring the difference of transmittance, and reading out the information based on the computer tomography technique (see PTL 2).
In the case of such recording media as CD and DVD, a laser beam is irradiated to the surface of the recording medium that is set on a rotating stage of a read out apparatus, while rotating the recording medium in a predetermined direction, and the reflected light, which changes depending on the convexoconcave structure on the surface of the recording medium, is detected, whereby the recorded information is read. In the case of an optical card as well, light is irradiated to a recording medium inserted into a read out apparatus, and the contrast of reflectance between a hole portion and a non-hole portion formed on the recording medium is detected, whereby the recording information is read out. To read out information recorded on such an information medium, the recording medium must be set in a correct position in the read out apparatus, such as the front surface/rear surface of the CD or DVD, and the insertion direction of an optical card. In the read out apparatus to read information recorded on the recording medium, the direction to read out the information is set based on the assumption that the recording medium is set in a correct position. Normally in such recording medium as a CD or DVD, a label surface constituted by a material that is different from the substrate of the recording medium is formed on one surface of the recording medium, and in such a recording medium as an optical card, a mark indicating the insertion direction is printed (For information on the optical card, see PTL 3). The operator can set the medium in the correct position in the read out apparatus by confirming the label surface or the mark.